The present invention relates generally to mobile communication systems and, more particularly, to methods for reducing power consumption by mobile terminals in mobile communication systems.
A known problem with WCDMA phones is excessive power consumption that results in undesirable current drain and short battery life. When engaged in normal voice communications, a WCDMA phone transmits and receives continuously. This continuous operation is one of the primary reasons for the undesirable current drain in WCDMA phones. Another reason for current drain is the presence of a duplexer in the transmit path that increases path loss.
The total output power of the mobile terminal can be reduced by using transmit diversity. With transmit diversity, the mobile terminal transmits signals on the uplink using two or more transmitters, each connected to their own antennas. Because of the resulting diversity gain, the mobile terminal generally requires less total transmit power when it uses multiple transmitters/antennas than when it uses a single transmitter/antenna. Thus, a mobile terminal using transmit diversity is generally more efficient than a mobile terminal that does not use transmit diversity.
However, this is true only when the mobile terminal operates at a high total output power. The efficiency diminishes when the total output power is low. Typically, a transmitter amplifier current drain level will typically not drop below some minimum level, even when the total output power is decreased below zero (0) dBm. This minimum current drain level is referred to as the “current floor.” When two transmitters are used for transmit diversity, this “current floor” is doubled. In this situation, the two transmitter amplifiers draw more current than a single amplifier.